power: fg/smbcharger:add support for PMI8940

PMI8940 uses the same fuel-gauge/charger block as PMI8950.
Add support of PMI8940 in order to configure charger/FG
based on PMIC.

CRs-Fixed: 1011021
Change-Id: Ifcdc893a6da3b7bd592d78c353b209ab264e5605
Signed-off-by: Ashay Jaiswal <ashayj@codeaurora.org>